These routines are included as a conversion aid for programs that use
the termcap library. Their parameters are the same and the routines
are emulated using the terminfo database. Thus, they can only be
used to query the capabilities of entries for which a terminfo entry
has been compiled.
The tgetent routine loads the entry for name. It returns:
1 on success,
0 if there is no such entry (or that it is a generic type, having
too little information for curses applications to run), and
-1 if the terminfo database could not be found.
This differs from the termcap library in two ways:
· The emulation ignores the buffer pointer bp. The termcap
library would store a copy of the terminal description in the
area referenced by this pointer. However, ncurses stores its
terminal descriptions in compiled binary form, which is not
the same thing.
· There is a difference in return codes. The termcap library
does not check if the terminal description is marked with the
generic capability, or if the terminal description has cursor-
The tgetflag routine gets the boolean entry for id, or zero if it is
The tgetnum routine gets the numeric entry for id, or -1 if it is not
The tgetstr routine returns the string entry for id, or zero if it is
not available. Use tputs to output the returned string. The area
parameter is used as follows:
· It is assumed to be the address of a pointer to a buffer
managed by the calling application.
· However, ncurses checks to ensure that area is not NULL, and
also that the resulting buffer pointer is not NULL. If either
check fails, the area parameter is ignored.
· If the checks succeed, ncurses also copies the return value to
the buffer pointed to by area, and the area value will be
updated to point past the null ending this value.
· The return value itself is an address in the terminal
description which is loaded into memory.
Only the first two characters of the id parameter of tgetflag,
tgetnum and tgetstr are compared in lookups.
The tgoto routine expands the given capability using the parameters.
· Because the capability may have padding characters, the output of
tgoto should be passed to tputs rather than some other output
function such as printf.
· While tgoto is assumed to be used for the two-parameter cursor
positioning capability, termcap applications also use it for
Doing this shows a quirk in tgoto: most hardware terminals use
cursor addressing with row first, but the original developers of
the termcap interface chose to put the column parameter first.
The tgoto function swaps the order of parameters. It does this
also for calls requiring only a single parameter. In that case,
the first parameter is merely a placeholder.
· Normally the ncurses library is compiled with terminfo support.
In that case, tgoto uses tparm(3X) (a more capable formatter).
However, tparm is not a termcap feature, and portable termcap
applications should not rely upon its availability.
The tputs routine is described on the curs_terminfo(3X) manual page.
It can retrieve capabilities by either termcap or terminfo name.
The variables PC, UP and BC are set by tgetent to the terminfo
entry's data for pad_char, cursor_up and backspace_if_not_bs,
respectively. UP is not used by ncurses. PC is used in the
tdelay_output function. BC is used in the tgoto emulation. The
variable ospeed is set by ncurses in a system-specific coding to
reflect the terminal speed.
Except where explicitly noted, routines that return an integer return
ERR upon failure and OK (SVr4 only specifies "an integer value other
than ERR") upon successful completion.
Routines that return pointers return NULL on error.
If you call tgetstr to fetch ca or any other parameterized string, be
aware that it will be returned in terminfo notation, not the older
and not-quite-compatible termcap notation. This will not cause
problems if all you do with it is call tgoto or tparm, which both
expand terminfo-style strings as terminfo. (The tgoto function, if
configured to support termcap, will check if the string is indeed
terminfo-style by looking for "%p" parameters or "$<..>" delays, and
invoke a termcap-style parser if the string does not appear to be
Because terminfo conventions for representing padding in string
capabilities differ from termcap's, tputs("50"); will put out a
literal “50” rather than busy-waiting for 50 milliseconds. Cope with
Note that termcap has nothing analogous to terminfo's sgr string.
One consequence of this is that termcap applications assume me
(terminfo sgr0) does not reset the alternate character set. This
implementation checks for, and modifies the data shown to the termcap
interface to accommodate termcap's limitation in this respect.
These functions are provided for supporting legacy applications, and
should not be used in new programs:
· The XSI Curses standard, Issue 4 describes these functions.
However, they are marked TO BE WITHDRAWN and may be removed in
· X/Open Curses, Issue 5 (December 2007) marked the termcap
interface (along with vwprintw and vwscanw) as withdrawn.
Neither the XSI Curses standard nor the SVr4 man pages documented the
return values of tgetent correctly, though all three were in fact
returned ever since SVr1. In particular, an omission in the XSI
Curses documentation has been misinterpreted to mean that tgetent
returns OK or ERR. Because the purpose of these functions is to
provide compatibility with the termcap library, that is a defect in
XCurses, Issue 4, Version 2 rather than in ncurses.
Compatibility with BSD Termcap
External variables are provided for support of certain termcap
applications. However, termcap applications' use of those variables
is poorly documented, e.g., not distinguishing between input and
output. In particular, some applications are reported to declare
and/or modify ospeed.
The comment that only the first two characters of the id parameter
are used escapes many application developers. The original BSD 4.2
termcap library (and historical relics thereof) did not require a
trailing null NUL on the parameter name passed to tgetstr, tgetnum
and tgetflag. Some applications assume that the termcap interface
does not require the trailing NUL for the parameter name. Taking
into account these issues:
· As a special case, tgetflag matched against a single-character
identifier provided that was at the end of the terminal
description. You should not rely upon this behavior in portable
programs. This implementation disallows matches against single-
character capability names.
· This implementation disallows matches by the termcap interface
against extended capability names which are longer than two
The BSD termcap function tgetent returns the text of a termcap entry
in the buffer passed as an argument. This library (like other
terminfo implementations) does not store terminal descriptions as
text. It sets the buffer contents to a null-terminated string.
This library includes a termcap.h header, for compatibility with
other implementations. But the header is rarely used because the
other implementations are not strictly compatible.
The original BSD termcap (through 4.3BSD) had no header file which
gave function prototypes, because that was a feature of ANSI C. BSD
termcap was written several years before C was standardized.
However, there were two different termcap.h header files in the BSD
· One was used internally by the jove editor in 2BSD through
4.4BSD. It defined global symbols for the termcap variables
which it used.
· The other appeared in 4.4BSD Lite Release 2 (mid-1993) as part of
libedit (also known as the editline library). The CSRG source
history shows that this was added in mid-1992. The libedit
header file was used internally, as a convenience for compiling
the editline library. It declared function prototypes, but no
The header file from libedit was added to NetBSD's termcap library in
Meanwhile, GNU termcap was under development, starting in 1990. The
first release (termcap 1.0) in 1991 included a termcap.h header. The
second release (termcap 1.1) in September 1992 modified the header to
use const for the function prototypes in the header where one would
expect the parameters to be read-only. This was a difference versus
the original BSD termcap. The prototype for tputs also differed, but
in that instance, it was libedit which differed from BSD termcap.
A copy of GNU termcap 1.3 was bundled with bash in mid-1993, to
support the readline library.
A termcap.h file was provided in ncurses 1.8.1 (November 1993). That
reflected influence by emacs (rather than jove) and GNU termcap:
· it provided declarations for a few global symbols used by emacs
· it provided function prototypes (using const).
· a prototype for tparam (a GNU termcap feature) was provided.
Later (in mid-1996) the tparam function was removed from ncurses. As
a result, there are differences between any of the four
implementations, which must be taken into account by programs which
can work with all termcap library interfaces.
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